let hd = {
  title: "后盾人",
  url: "houdunren.com",
  teacher: {
    name: "向军大叔"
  }
};
//第二个参数是一个数组，需要的属性字符串放里面
let json = JSON.stringify(hd, ["title", "url"], 4);
console.log(json);
